Electronic devices may be formed on thin-film silicon-on-insulator (SOI) substrates with reduced short-channel effects, reduced parasitic and nodal capacitances, increased radiation hardness and reduced process complexity compared to bulk semiconductor devices. However, SOI devices may have parasitic contact resistances, such as high source and drain contact resistances to SOI MOSFETs. These difficulties in using thin-films are disclosed in an article by L. Su., M. Sherony, H. Hu, J. Chung and D. Antoniadis, entitled "Optimization of Series Resistance in Sub-0.2 .mu.m SOI MOSFETs", International Electron Devices Meeting (1993), No. 30.1.1-30.1.4, pp. 723-726. Accordingly, there is a need for improved interconnects which have low resistance characteristics and which are compatible with thin-film processing techniques.
To address this need, methods for forming epitaxial metal silicides have been developed because of their relatively low electrical resistance, low contact resistivity and high thermal stability. In particular, cobalt-disilicide has been considered attractive as an epitaxial layer on silicon because of its thermal stability and close lattice match with silicon (1.07% smaller than silicon at room temperature). These benefits and a method of forming CoSi.sub.2 on silicon are disclosed in an article by M. Lawrence, A. Dass, D. Fraser and C. Wei, entitled Growth of epitaxial CoSi.sub.2 on (100) Si, Appl. Phys. Lett. 58 (12), pp. 1308-1310 (1991). Coinventors T. Tan and G. McGuire also disclose the formation of epitaxial CoSi.sub.2 on bulk silicon substrates in an article entitled Formation of epitaxial CoSi.sub.2 films on (001) silicon using Ti-Co alloy and bimetal source materials, J. Appl. Phys. 70 (12), pp. 7579-7587 (1991), the disclosure of which is hereby incorporated herein by reference.
Unfortunately, these methods for forming epitaxial metal-disilicide films may have shortcomings. For example, in the aforementioned article by L. Su, et al., the series resistance of cobalt-disilicide films was found to increase dramatically once the silicide fully consumed the underlying silicon layer. The disclosed reason for the increase in resistance was the conversion of CoSi.sub.2 to metal-rich CoSi and the reduction in contact area once the silicon layer was fully consumed. These authors disclose that to achieve low parasitic series resistance, very thin silicides are required which do not fully consume the silicon underlayer of a SOI substrate.
Thus, notwithstanding these attempts to form silicides on bulk silicon and SOI substrates, there continues to be a need for a method of forming low-resistance metal-disilicide films on SOI substrates which does not cause the formation of metal-rich silicides and which achieves low parasitic series resistance.